<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        div {
            width: 100px;
            height: 100px;
            border: 1px solid red
        }

        #d1 {
            position: absolute; /*绝对定位*/
            /*默认以窗口为参照物进行偏移*/
            bottom: 0px;
            right: 0px;
        }
        #big{
            width: 200px;height: 200px;background-color: green;
            margin: 100px 0 0 100px;
            position: relative;/*做参照物*/
        }
        #big>div{
            width: 100px;height: 100px;background-color: blue;
            margin: 30px 0 0 30px;
        }
        #big>div>div{
            width: 50px;height: 50px;background-color: red;
            position: absolute;
            top: 0;
            left: 0;
        }
    </style>
</head>
<body>
<div id="big">
    <div>
        <div></div>
    </div>
</div>
<div id="d1">div1</div>
<div>div2</div>
<div>div3</div>
</body>
</html>